Method of welding silicon steel



United States Patent 3,142,116 METHOD OF WELDING SILICON STEEL Sadayoshi Morita and Teiji Ito, Yawata, and Ariuobu Yainada, Tobata, Japan, assignors to Yawata Iron &

Steel Co, Ltd., Tokyo, .lapan, a corporation of Japan No Drawing. Filed Apr. 9, 1962, Ser. No. 185,870

Claims priority, application Japan Apr. 14, 1961 2 Claims. (Cl. 29-480) The present invention relates to a method of welding silicon steel strip in making silicon steel plate for electromagnetic materials.

In making silicon steel plate 0.5 mm. thick or under at present, a manufacturing process is sometimes used where the silicon strips about 1.0 mm. thick are welded together and then subjected to cold rolling. In such welding, a tungsten inert-gas arc welding process has usually been adopted using an ordinary tungsten electrode and because of the steel plate being too thin the so-called non filler metal process has been used without using a welding rod. The weld metal portion melted by welding heat in the welding method currently in use shows conspicuous development of columnar crystals, particularly when the metal plate, which has a ferrite structure even in a high temperature range, is concerned, and in such case the structure of the weld metal portion tends to become very coarse and in consequence often liable to cause breakage at the weld metal portion in cold rolling process subsequent to welding.

The first characteristic feature of the present invention comprises using, as a welding rod, mild steel core wire low in silicon content for minimizing the silicon content of weld metal portion in order to prevent the same from becoming coarse and to minimize the risk of breakage liable to occur at the weld metal portion. By using a mild steel welding rod of chemical composition as shown in Table 1, the silicon content of the weld metal portion is minimized as much as possible and its structure is austenitized at higher temperature and the structure of the weld metal portion can be made pearlite or a mixture of pearlite and ferrite of columnar crystal in the finest possible crystal grains.

If the carbon content of the welding rod and core wire used in this welding method exceeds 0.2% as shown in Table 1, the structure of the weld steel tends to become martensite, harder and more brittle owing to relatively faster cooling at the weld part. And also, the border part tends to grow an anomalous structure of SiC and particularly mechanical properties such as flexural strength and elongation deteriorate. Furthermore, the lower its silicon content is, the more fine-grained becomes the structure of the weld steel and the mechanical properties such as elongation and toughness are improved.

Table 1 Chemical composition of welding rod (percent) 0.2 2.0 0.03 0.03 0.03 regiainof the normal thickness of the plate and then levelling it oil smooth by rolling.

In the so-called non filler metal Welding process," the surplus thickness is so small because of the welding rod being not used, that the weld plate can be rolled without going through a scraping process, but the weld portion tends to become unshapely compared with the base metal and is liable to become a cause of breakage of steel strip owing to an instantaneous impact being added to the weld metal portion at the time of rolling.

In welding by the method of this invention, the weld metal portion will have a greater surplus thickness because of the welding rod being used compared with the weld metal portion obtained by the so-called non filler metal process, but the chemical composition of the weld metal portion, which is almost the same as that of mild steel, will present no problem in processes such as scraping, grinding and rolling. And such weld metal portion, ground to a thickness equal to or slightly in excess, even for example, of the thickness of the base plates, can be made substantially equal in thickness to that of the base plate by rolling and trimmed free from any surface defects preventing thus impact on the Weld metal portion which is likely to occur at the time of rolling and in consequence the risk of breakage is completely eliminated. If the weld metal portion is less than 115% of the base plates in thickness, it can be made level and smooth only by rolling without going through a scraping process.

The third characteristic feature of this invention comprises the process in which a weld metal portion ground or scraped down to a thickness equal to that of the base metal after welding is subjected to rolling by means of upper and lower rotary plate rolls while applying an appropriate voltage between the rolls and directly supplying electric current to and heating the said weld metal portion to a suitable temperature as stated below with results of homogenizing the structures of the weld metal portion and its adjoining area and properly trimming the weld metal portion. That is to say, even when a welding rod was used, the weld metal portion has a columnar structure remaining after welding, and the weld metal portion is liable to break on account of lack of sufiicient strength to endure the external force of impact at the time of cold rolling. But, by directly supplying electric current to and rolling the weld metal portion its columnar structure was homogenized and standardized, particularly improving elongation and toughness of the weld metal portion so that it retained sufficient strength to endure external force at the time of cold rolling.

As stated above, the third characteristic feature of this invention lies in destroying and finely granulating austenite grains, etc. at the weld metal portion at high temperature and the rolling force must be selected according to the thickness of the plate. As the thickness of plate increases, rolling force must be increased.

For example, the following relation between rolling force and plate thickness must exist when the plate is finely granulated uniformly as far as its interior:

Rolling force (total pressure applied), kg.

Plate thickness It is necessary to apply rolling force while heating in the austenite region up to a temperature in excess of the A3 transformation point, not only by direct electric heating, but also by any appropriate means such as gas fire, high-frequency heating, etc.

The diameter, wall thickness and material of the rotary plate roll are subject to some alteration according to thickness and quality, etc. of the welded plate, but in the case of a steel roll it should be more than 500 HV in hardness of the peripheral face, more than 200 mm. in diameter,

and more than 13 mm. in wall thickneses, of which particularly the wall thicknes should be properly selected in accordance with the width of the weld bead. Table 2 below shows the comparative results of welding experiments on the cold rolled silicon steel strips 0.7 mm. thick obtained by using a conventional method and the method of this invention, such as the difference in welding conditions and breakage rates of the weld metal portion at the time of cold-rolling.

As clearly seen in this table, the welding by the invention method shows remarkably improved results in which the rate of breakage is reduced to nothing.

CI'IEhHCAL COMPOSITION OF WELDING ROD USED IN THE WELDING EXPERIMENT (PERCENT) 0. G8 0.25 0. 03 O. 03 Re mainder.

The third characteristic feature of this invention as above mentioned has been verified from experiments to show very valuable results when the plates are of greater Table 2 thickness and also when the welding is made by an inertgas arc welding method or by a submerged arc welding WCKL W91 WOW Diameter Feeding method. That 1s as tne plate increases 1n thickness, the I ing ing jug Argon of me or chemical composition of tne weld metal by MIG. method Woldmg common gigg $85 5 lg gf fi or by Submerged arc welding method will be influenced mini) m 1pm,) less by the base material than that of the weld metal made by the T.I.G. method using a welding rod, and will re- Conventional semble the composition of the welding core wire used,

11-12 90 thereby making the first characteristic feature of this inthis invention so 12-13 90 12 0. s1 s4 vention display its advantage. However, even in this case elongation and toughness of the weld metal portion will be still further improved, if the process of electric rolling Width of Diameter Traveling Temper- 1S adoptefi' Conditionof rotary olrotary Rolling rate of ature at Referring to Table 3 showing the experiment results 51 5 55 233? 1135;? fifgg of welding cold rolled silicon steel plates 1.8 mm. thick, 1t will be realized that by adopting the process of rolling with electric power supplied, the elongation of the weld Convehnttiional 40 portion is greatly improved and by using the method of gg g g this invention such an excellent welding of silicon steel vention used... 13 00 0 90 870-920 strips will be achieved that they can easily endure cold rolling.

Table 3 Welding Welding Rate of Argon Diameter of core Welding condition current used voltage used welding flow Flux wire (mm. qb)

(Amp) (Volt) (cm/mm.) (l./min.)

MIG welding 125-205 26-28 110-120 10 1.0. Submerged arc welding 260 23 200 Grade 55 2.4.

Il1(O)5l1 12 x 15 Condition of rolling with eleetr. Roll Width Roll diam. Rolling Pres- Roll travel Temperature used supplying. (mm). (mm. sure (kg). rate (cm./ in process 01 rollmin.) ing with clectr.

supplying 0.). Conventional method use Method of this invention 13 200 1,500 880-930.

Elongation Repeating Mechanical properties of weld portion (percent) bending test value 5R Base material.- 1.0 O. MIG welding:

Untreated. 4. 0 2. 5 Treated under this invention 12 2 7. 5 Submerged arc welding process:

Untreated u c u 4. 5 3. 0 Treated under this invention 13. 5 8. 4

Chemical composition of core wire used n) 0 Mn Sr P S Sol. Al Insol, A1

For MIG welding 0.147 0. 33 0. 01 0. 00 0. 015 0. 003 on 00 For Submerged arc welding 0. 08 0.25 0. 03 0. 03 0.03 0.002 0.005

5 6 What we claim is: being heated up to said temperature by directly supplying 1. A method of Welding silicon steel plate comprising electric current thereto. the steps of welding silicon steel plates by using a mild steel welding rod containing below 0.2% C and below References Cited in the file of this Patent 0.03% Si, leveling off and trimming the surplus thickness 5 UNITED STATES PATENTS and then subjecting the welded portion and its adjoining region to roll press while heating it at a temperature in fi ii excess of the A3 transformation point but below the 21766O2 Ong Be Beck et a1 Oct. 17, 1939 Z d 1 d 1 1 h th 1d 2,231,014 Lytle et a1 Feb. 11, 1941 me 0 as calme 1n calm In W 10 e We ll Dec. 31,

portion and its adjoining region are roll pressed while 

1. A METHOD OF WELDING SILICON STEEL PLATE COMPRISING THE STEPS OF WELDING SILICON STEEL PLATES BY USING A MILD STEEL WELDING ROD CONTAINING BELOW 0.2% C AND BELOW 0.03% SI, LEVELING OFF AND TRIMMING THE SURPLUS THICKNESS AND THEN SUBJECTING THE WELDED PORTION AND ITS ADJOINING REGION TO ROLL PRESS WHILE HEATING IT AT A TEMPERATURE IN EXCESS OF THE A3 TRANSFORMATION POINT BUT BELOW THE SOLIDUS POINT. 